An important aspect of any mobile communications system is to determine the position of each mobile radio in order to provide one or more services that involve the mobile radio. Indeed, the central feature of mobile communications is “mobility,” and mobility is managed by a radio network operator based on the radio network being aware of the current location of each mobile radio. Mobile location information allows the radio network to page the mobile terminal and route a mobile-terminating call to wherever the mobile terminal is located. It also allows visiting networks to provide service to mobile radios.
Typically, a mobile terminal registers with the network each time it enters a new location area, registration area, paging area, or cell. That location is still a fairly coarse measurement depending on the size of that area/cell. The larger the area/cell, the less accurate the location information for the mobile radio. In addition, there are good reasons not to have the mobile terminal send registration messages every time it enters or leaves a relatively small sized area/cell including reduced signaling overload across the radio interface and reduced administration associated with handling a larger volume of registration messages.
Even if the mobile radio reports its position at the cell level, that position is still not particularly accurate. This accuracy is further undermined when the mobile radio is communicating with a set of cells, i.e., having a mobile connection in a diversity handover situation. This set of cells is called the active set. Base station transmissions from cells in the active set, and from “candidate cells” for the active set, are measured by the mobile station. The mobile station updates its active set based upon the signal quality or signal strength of the measured signals of the active set cells and candidate cells. Having multiple cells support a mobile connection makes it unclear in which of the cells the mobile radio is actually located. One approach is to assume the mobile radio is located in the active set cell with the highest signal strength/lowest path loss. However, this approach involves assumptions and relies on measurements made by the mobile radio and communicated to the radio network. The assumptions may be wrong, the measurements may be inaccurate, and the communication over the radio interface may be corrupted.
It would therefore be desirable to have a more reliable and accurate way to determine the position of a mobile radio that is not complicated, expensive, or time consuming. Such a determination preferably should not depend on measurements made by the mobile radio. Ideally, the method of determining a mobile's position should be able to take advantage of information relating to cells currently in a mobile's active set.
The present invention uses cell location information available in the radio network to determine an area where the mobile radio is located and does not rely upon mobile radio measurements. Such cell location information for cells currently associated with the mobile radio is used by the radio network to determine a location of the mobile radio. Those current cells may include, for example, cells that are members of or candidates for an active set of cells, cells that are currently supporting communication with the mobile radio in diversity handover, or some other group of cells geographically associated with the mobile radio. The cell location information defines one or more boundaries of each cell and is stored in the radio network. Coordinates of the boundary positions for each of the cells currently associated with the mobile radio are used to define the mobile location.
A boundary position includes a horizontal coordinate and vertical coordinate. The horizontal coordinates of all available boundary positions are compared, and one or more of them is selected. Similarly, the vertical coordinates for each cell in the known. Non-limiting examples of cells includes: macro-cells, micro-cells, pico-cells, registration areas, location areas, base station cells, and base station sector cells.